Quantentechnologie

2002

• B. Ueberholz, S. Kuhr, D. Frese, V. Gomer and D. Meschede
  Cold collisions in a high-gradient magneto-optical trap, J. Phys. B: At. Mol. Opt. Phys. 35, 4899 (2002)BibTeX
  ABSTRACT »

  We present a detailed analysis of the cold collision measurements performed in a high-gradient magneto-optical trapwith a few trapped Cs atomsfirst presented in Ueberholz et al (J. Phys. B: At.Mol. Opt. Phys. 33 (2000) L135). The ability to observe individual loss events allows us to identify two-body collisions that lead to the escape of only one of the colliding atoms (up to 10% of all collisional losses). Possible origins of these events are discussed here. We also observed strong modifications of the total loss rate with variations in the repumping laser intensity. This is explained by a simple semiclassical model based on optical suppression of hyperfine-changing collisions between ground-state atoms.

2001

• V. Gomer and D. Meschede
  A single trapped atom: Light-matter interaction at the microscopic level, Ann. Phys. (Leipzig) 10, 9-18 (2001)BibTeX
  ABSTRACT »

  For a single trapped atom the fluctuations of resonance fluorescence reveal its dynamic evolution at all relevant time scales. We review experimental results, extend interpretations and express expectations for future systems with fully controlled quantum properties.

2000

• H. Schadwinkel, V. Gomer, U. Reiter, B. Ueberholz and D. Meschede
  Quantum Fluctuations of a Single Trapped Atom: Transient Rabi Oscillations and Magnetic Bistability, IEEE J. of Quantum Electronics 36, 1358 (2000)arXivBibTeX
  ABSTRACT »

  Isolation of a single atomic particle and monitoring its resonance fluorescence is a powerful tool for studies of quantum effects in radiation-matter interactions. We present observations of quantum dynamics of an isolated neutral atom stored in a magneto-optical trap. By means of photon orrelations in the atom's resonance fluorescence we demonstrate the well-known phenomenon of photon antibunching which corresponds to transient Rabi oscillations in the atom. Through polarization-sensitive photon correlations, we show a novel example of resolved quantum fluctuations: pontaneous magnetic orientation of an atom. These effects can only be observed with a single atom.

• B. Ueberholz, S. Kuhr, D. Frese, D. Meschede and V. Gomer
  Counting Cold Collisions, J. Phys. B: At. Mol. Opt. Phys. 33, L135 (2000)arXivBibTeX
  ABSTRACT »

  We have experimentally explored a novel possibility to study exoergic cold atomic collisions. Trapping of small countable atom numbers in a shallow magneto-optical trap and monitoring of their temporal dynamics allows us to directly observe isolated two-body atomic collisions and provides detailed information on loss statistics. A substantial fraction of such cold collisional events has been found to result in the loss of one atom only. We have also observed for the first time a strong optical suppression of ground-state hyperfine-changing collisions in the trap by its repump laser field.

1999

• H. Schadwinkel, U. Reiter, V. Gomer and D. Meschede
  Magneto-optical trap as an optical lattice, Phys. Rev. A 61, 013409 (1999)BibTeX
  ABSTRACT »

  We study the magneto-optical trap (MOT) as an optical lattice with a setup providing full phase control for all light fields. Although completely different light fields are possible for various phases, we have found experimental evidence that stored atoms are generally localized in micropotentials of the six-beam lattice. The influence of the phase variation is surprisingly small, suggesting that the robust behavior of the MOT is a consequence of this fact. We find furthermore good agreement of our experimental data with a simple theoretical model which reduces the complicated MOT to a description of steady-state atoms localized at points of the deepest adiabatic light-shift potential.

1998

• V. Gomer, F. Strauch, B. Ueberholz, S. Knappe and D. Meschede
  Single-atom dynamics revealed by photon correlations, Phys. Rev. A 58, R1657 (1998)BibTeX
  ABSTRACT »

  We have studied a single neutral atom stored in a magneto-optical trap by recording arrival times of fluorescence photons emitted by the atom. Photon correlations at nanosecond scales (Rabi oscillations), at microseconds (intensity and polarization correlations), and also at milliseconds (position correlations) reveal the dynamical behavior of the atomic excitation, of the atomic orientation, and of its transport in the trap at both the optical wavelength scale and the trap size.

• V. Gomer, B. Ueberholz, S. Knappe, F. Strauch, D. Frese and D. Meschede
  Decoding the dynamics of a single trapped atom from photon correlations, Appl. Phys. B 67, 689 (1998)BibTeX
  ABSTRACT »

  Information on the dynamics of a single neutral atom can be decoded from fluctuations in the resonance fluorescence. We have measured two-time photon correlations of individual cesium atoms stored in a magneto-optical trap. We observe strong correlations at nanosecond scales (Rabi oscillations), at microseconds (intensity and polarization correlations), and also at milliscconds (position correlations) revealing the dynamical behavior of the atomic excitation, of the atomic orientation, and of its transport in the trap at both the optical wavelength scale and the trap size. In this article we compare our experimental results with a simplified model of an atom moving through an optical lattice. We investigate the influence of light-field topogaphy and of the multilevel character of the atom on the shape and the visibility of the correlations.

• A. Rauschenbeutel, H. Schadwinkel, V. Gomer and D. Meschede
  Standing light fields for cold atoms with intrinsically stable and variable time phases, Opt. Comm. 148, 45 (1998)BibTeX
  ABSTRACT »

  We present a novel method to realise a standing light field with a stable configuration in two or three dimensions. A single standing wave formed by two counterpropagating beams is folded and brought into intersection with itself. The values of the relative timephases are stable, a priori known, and can be altered arbitrarily by means of retardation plates. The polarisation configurations of three orthogonal standing waves include the standard magnetooptical trap and a novel three-dimensional pure polarisation lattice which we have investigated in a first spectroscopic measurement, providing strong evidence for atomic localisation in both cases.

1997

• D. Meschede, I. Bloch, A. Goepfert, D. Haubrich, M. Kreis, F. Lison, R. Schuetze and R. Wynands
  Atom optics with permanent magnetic components, Proc. SPIE 2995, Atom Optics 2995, 191 (1997)BibTeX
  ABSTRACT »

  We have fabricated and investigated efficient magnetic lenses, waveguides, and mirrors from rare earth permanent materials. They are affordable and maintenance free. In contrast to corresponding light force components they do not need any supplies, they have large apertures, high reflectivity, and there is no spontaneous emission. The cylindrical shape of magnetic components is furthermore well suited to steer atomic beams.

• F. Strauch, V. Gomer, H. Schadwinkel, B. Ueberholz, D. Haubrich and D. Meschede
  Diffraction by cold atoms, Opt. Comm. 145, 57 (1997)BibTeX
  ABSTRACT »

  We have observed diffraction of a laser probe beam by a trapped sample of cold atoms. The effect is only visible in the vicinity of a resonance line. The observed diffraction pattern arises from interference of the incident and scattered light wave, allowing reconstruction of geometric properties of the trapped sample from the holographic record.

• V. Gomer, O. Harms, D. Haubrich, H. Schadwinkel, F. Strauch, B. Ueberholz, S. aus der Wiesche and D. Meschede
  Magnetostatic traps for charged and neutral particles, Hyperfine Interactions 109, 281-292 (1997)BibTeX
  ABSTRACT »

  We have constructed magnetostatic traps from permanent magnets for trapping charged and neutral atoms. Two storage experiments are presented: a compact Penning trap for light ions and magnetic trapping of single neutral atoms. The dynamics of cold neutral atoms and their loss mechanisms in a quadrupole magnetostatic trap are discussed.

1996

• D. Haubrich, H. Schadwinkel, F. Strauch, B. Ueberholz, R. Wynands and D. Meschede
  Observation of individual neutral atoms in magnetic and magneto-optical traps, Europhys. Lett. 34, 663 (1996)BibTeX
  ABSTRACT »

  We have identified and photographed individual cesium atoms in a magneto-optical trap with steep magnetic gradients. By switching off the trapping light fields, single atoms were released to a bound state of the magnetic potential. A storage time of 38 s was measured for purely magnetic trapping, whereas a storage time of 147 s was observed in the corresponding magneto-optical trap.

• W. G. Kaenders, F. Lison, I. Müller, A. Richter, R. Wynands and D. Meschede
  Refractive components for magnetic atom optics, Phys. Rev. A 54, 5067 (1996)BibTeX
  ABSTRACT »

  With strong rare-earth permanent magnets we have built highly refractive atom-optical components for laser-cooled atoms. We have studied the influence of axially symmetric multipole components on a cesium atomic beam. In analogy to traditional optics the action of a quadrupole ring parallels a conical prism, or axicon. Hexapole lenses were applied for focusing with a more than 1000-fold increase in atomic flux density at the focal spot and for imaging with the atomic beam. Two hexapole lenses were combined to form a telescope, which was operated off axis in order to separate fast thermal and slowed atoms. The experiments can approximately be described in terms of geometrical optics.

1994

• A. Höpe, D. Haubrich, H. Schadwinkel, F. Strauch and D. Meschede
  Optical Trapping in a Cesium Cell with Linearly Polarized Light and at Zero Magnetic Field, Europhys. Lett. 28, 7 (1994)BibTeX
  ABSTRACT »

  We have found that linearly polarized light can be used efficiently for optical trapping of cesium atoms in a magnetic-quadrupole field. The number and density of atoms of the trapped samples are comparable to a standard magneto-optical trap with σ⁺ - σ^– polarized light, but the influence of the magnetic-quadrupole strength is strikingly different. When the polarization of counterpropagating light beams is orthogonal, trapping is observed also for zero magnetic field.

1993

• A. Höpe, D. Haubrich, G. Müller, W. G. Kaenders and D. Meschede
  Neutral Cesium Atoms in Strong Magnetic-Quadrupole Fields at Sub-Doppler Temperatures, Europhys. Lett. 22, 669 (1993)BibTeX

• D. Haubrich, A. Höpe and D. Meschede
  A simple model for optical capture of atoms in strong magnetic quadrupole fields, Opt. Commun. 102, 225 (1993)BibTeX

• W. G. Kaenders, V. Frerichs, F. Schröder and D. Meschede
  Pure multipoles from strong permanent magnets: analytic and experimental results, Hyperfine. Interact. 76, 221 (1993)BibTeX
  ABSTRACT »

  We present the construction of arbitrary multipole field configurations from strong permanent magnets for trapping charged or neutral particles. A general analytic method for the design of three-dimensional magnetic multipoles is discussed for an idealized continuously varying magnetisation taking advantage of the superposition principle. Simple recipes for constructing magnetic dipole and quadrupole fields are given with two types of elements, axially and radially magnetised rings. Cylindrical magnet components not only give free access to the experimental region of interest, but also allow for some tunability to reduce undesirable higher multipole orders. Measurements confirm theoretical predictions achieving useful magnetic fields of 1 T and steep gradients of 3 T/cm with high purity over several ccm.

1992

• V. Frerichs, W. G. Kaenders and D. Meschede
  Analytic construction of magnetic multipoles from cylindric permanent magnets, Applied Physics A Solids and Surfaces 55, 242--249 (1992)BibTeX
  ABSTRACT »

  We discuss an analytic method for the design of three-dimensional magnetic multipoles from permanent magnet materials. The concept is explicited with an idealized, continuously varying magnetization. The effect of segmentation for realistic implementations is discussed. As an example we present an open, experimentally accessible cylindric structure for a dipole and a quadrupole field with high purity. The fields are useful over several cm³.